Functional coating with low contact resistance and high corrosion resistance and preparation method

Abstract

The invention relates to the technical field of hydrogen production, in particular to a low-contact-resistance and high-corrosion-resistance functional coating and a preparation method thereof.The low-contact-resistance and high-corrosion-resistance functional coating comprises a transition layer and an outer layer, and the outer layer is made of C-element-containing corrosion-resistant metal. As the bipolar plate coating does not contain noble metal elements, the bipolar plate coating provided by the invention is low in cost, and the manufacturing cost of the PEM hydrogen production electrolytic cell can be reduced.

Description

Technical Field

[0001] This invention relates to the field of hydrogen production technology, specifically to a functional coating with low contact resistance and high corrosion resistance, and its preparation method. Background Technology

[0002] Proton exchange membrane (PEM) electrolysis of water is a highly efficient and environmentally friendly hydrogen production technology and an important direction for hydrogen production through water electrolysis. Among the components, the bipolar plate is a key component of the PEM electrolyzer, accounting for 60-80% of the weight of the stack and approximately 40% of the cost. Simultaneously, the bipolar plate plays a crucial role in current collection, conductivity, and connecting individual modules. Therefore, an ideal bipolar plate must possess excellent thermal conductivity, electrical conductivity, and mechanical properties. Metal bipolar plates have been extensively studied due to these properties. However, the operating environment of a PEM electrolyzer is acidic (pH≈2-5) and at relatively high temperatures (60-80°C). o C) and the voltage is relatively high (1.4–2.2V vs SHE). In this environment, the metal bipolar plates are easily corroded, thus shortening the stack's lifespan. Furthermore, the oxide film formed on the metal surface has low conductivity, increasing the interfacial contact resistance between the bipolar plates and the gas diffusion layer, further increasing ohmic losses. Therefore, developing low-resistance, highly corrosion-resistant coatings on the bipolar plate surface is crucial.

[0003] Currently, the coating materials used on the surface of bipolar plates in PEM electrolytic cells are mostly noble metals (Pt, Ru, Ir, etc.), nitrides (TiN, CrN, etc.), conductive oxides (Ti4O7, indium tin oxide, etc.), and other corrosion-resistant coatings. Noble metal coatings have good corrosion resistance and conductivity, which can significantly improve the overall performance of bipolar plates. However, the high price of noble metals leads to a significant increase in manufacturing costs, thus limiting their commercial application. Nitride coatings exhibit excellent conductivity, but they dissolve at high potentials and lose their protective effect, thus limiting their large-scale application. Conductive oxide coatings suffer from complex manufacturing processes, poor process stability, and high costs. Metal-based coatings have good application value in bipolar plate applications due to their advantages in material cost and manufacturing processes, but they suffer from increased contact resistance caused by corrosion and oxidation. Summary of the Invention

[0004] The purpose of this invention is to provide a functional coating with low contact resistance and high corrosion resistance and a preparation method thereof, thereby solving the technical problem of increased contact resistance caused by corrosion and oxidation in existing metal-based coatings.

[0005] This invention discloses a functional coating with low contact resistance and high corrosion resistance, comprising a transition layer and an outer layer, wherein the outer layer is a corrosion-resistant metal containing carbon.

[0006] Furthermore, in atomic percentage terms, the corrosion-resistant metal accounts for 70-98%, and the carbon element accounts for 2-30%.

[0007] Furthermore, the corrosion-resistant metal is at least one of the metal elements Nb, Ta, Zr, or Hf.

[0008] Furthermore, the transition layer metal is one or more of Zr, Nb, Ta, and Hf.

[0009] Furthermore, the transition layer is coated on the bipolar plate.

[0010] Furthermore, the bipolar plate is a titanium bipolar plate.

[0011] A method for preparing a bipolar plate coating with low contact resistance and high corrosion resistance, wherein the preparation method is DC magnetron sputtering.

[0012] Furthermore, the DC magnetron sputtering includes the following steps: A transition layer is prepared on a bipolar plate by sputtering a metal target, and then an outer layer is deposited by co-sputtering a metal target and a graphite target, or a metal target and a metal / graphite composite target, or a metal / graphite composite target.

[0013] Furthermore, when preparing the transition layer by sputtering a metal target, the metal target material is one or more of Zr, Nb, Ta and Hf, and the purity of the target material is higher than 99.9%.

[0014] Furthermore, when preparing the outer layer by co-sputtering a metal target and a graphite target, the metal target material is one or more of Zr, Nb, Ta and Hf, and the purity of the target material is higher than 99.9%, and the purity of the graphite target is higher than 99.9%.

[0015] Furthermore, when preparing the outer layer by co-sputtering a metal target and a metal / graphite composite target, the metal target material is one or more of Zr, Nb, Ta and Hf, the purity of the target material is higher than 99.9%, the impurity element content of the metal / graphite composite target is less than 0.1%, and the graphite atom content accounts for 10-50% of the metal / graphite composite target.

[0016] Furthermore, when preparing the outer layer by sputtering a metal / graphite composite target, the metal is one or more of Zr, Nb, Ta and Hf, the impurity element content of the metal / graphite composite target is less than 0.1%, and the graphite content accounts for 2-30% (atomic percentage).

[0017] Furthermore, the bipolar plate is etched under vacuum conditions using Ar plasma before sputtering the transition layer, and Ar is used as the working gas during sputtering the transition layer.

[0018] Furthermore, the vacuum condition is that the background vacuum of the vacuum chamber is less than 5 × 10⁻⁶.-3 Pa, the distance between the surface of the bipolar plate and the sputtering target is 5-15cm.

[0019] Furthermore, when performing Ar plasma etching on the bipolar plate, either an ion source-assisted method or a method of applying a high negative bias voltage to the bipolar plate can be used, with the bias voltage being less than -450V.

[0020] Furthermore, the bipolar plate is cleaned and decontaminated before etching.

[0021] Furthermore, the bipolar plate cleaning and decontamination treatment employs organic solvents, alkaline cleaning solutions, or ultrasonic cleaning with water.

[0022] Compared with the prior art, the beneficial effects of the present invention are: 1. Because it does not contain precious metal elements, the bipolar plate coating provided by this invention has low cost, which can reduce the manufacturing cost of PEM hydrogen electrolyzers; 2. By rationally selecting the composition of the metal / graphite composite target, the present invention can improve the coating production efficiency by sputtering multiple composite targets simultaneously. The coating preparation method provided by the present invention is suitable for establishing a continuous and stable production line. 3. The conductivity and corrosion resistance of this invention are superior to those of corresponding single-layer metal coatings, and the surface contact resistance of the bipolar plate decreases significantly after corrosion. The dual-layer coating effectively improves the electrolysis efficiency and service life of the PEM water electrolysis hydrogen production electrolyzer. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the coating structure of the present invention.

[0025] Figure 2 This is a potentiodynamic polarization curve of the Ta / Ta-C coating of the present invention.

[0026] Figure 3 This is a potentiostatic polarization curve of the Ta / Ta-C coating of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0028] Example 1 This embodiment discloses a functional coating with low contact resistance and high corrosion resistance, and its preparation method, including the following steps: (1) The metal titanium bipolar plate with flow channel, which is about 2 mm thick and machined, is ultrasonically cleaned in ethanol and petroleum ether to remove surface oil and debris.

[0029] (2) Fix the cleaned titanium bipolar plate on the sample holder and transfer it to the working position in the sputtering coating chamber. When the surface of the bipolar plate is parallel to the target surface, the distance between them is 10 cm. After closing the coating chamber, evacuate it. When the chamber pressure is less than 5.0 × 10⁻⁶ cm, the pressure is controlled to be within 10 cm. -3 At a pressure of Pa, Ar is introduced into the chamber, and the chamber vacuum is maintained at approximately 0.1 Pa. After the gas pressure stabilizes, a -600V pulsed DC bias is applied to the surface of the bipolar plate for plasma etching, which takes 30 minutes.

[0030] (3) After plasma etching, the target cathode power supply is turned on to deposit the coating. The coating chamber is equipped with four DC magnetron cathodes, with two metal Ta targets and two graphite targets installed respectively. The coating deposition process adopts the target current control mode. First, the Ta target cathode power supply is turned on to deposit the metal Ta transition layer, with a target current of 5.0A and a deposition time of 30 minutes; then, the Ta and graphite target cathode power supplies are turned on to co-sputter and deposit the metal Ta-C composite outer layer. The metal Ta and graphite target currents are set to 5.0A and 0.4A respectively, the bias voltage is -200V, the deposition gas pressure is about 0.3Pa, and the deposition time is 180 minutes. During the deposition process, the bipolar plate triaxial gantry rotates on the triaxial hanger at a speed of 10 rpm. After the coating is completed, it is naturally cooled until the vacuum chamber temperature is below 80℃, the vacuum chamber is filled with gas, the chamber is opened, and the sample is taken out.

[0031] In this embodiment, its structure is as follows: Figure 1 As shown, the deposited coating consists of a Ta transition layer and a Ta-C composite outer layer. The thickness of the metallic Ta transition layer is approximately 400 nm, and the thickness of the Ta-C composite outer layer is approximately 2.7 μm. The outer layer contains approximately 96.4% Ta and 3.6 at.% C atomically. The initial contact resistance between the coating and the carbon paper was measured to be 5.2 mΩ·cm under a pressure of 1.2 MPa. 2 Under harsh simulated PEM hydrogen production conditions (0.5 MH2SO4 + 5 ppm HF, 80...), o C) To evaluate the corrosion resistance of the coating, the corrosion current density of the coating was measured to be 0.190 μA / cm² using potentiodynamic polarization. 2 ( Figure 2 The current density during the 24-hour potentiostatic polarization test was 0.1 μA / cm. 2 ( Figure 3 The surface contact resistance after testing was 476 mΩ·cm. 2 .

[0032] Example 2 This example, as a preferred embodiment of the present invention, discloses a functional coating with low contact resistance and high corrosion resistance and its preparation method. The only change from Example 1 is the sputtering current of the graphite target. The outer layer has a Ta element content of 92.3% and a C element content of 7.7% by atomic percentage.

[0033] In this embodiment, the sputtering currents for the Ta target and the graphite target were 5.0 A and 0.8 A, respectively. The deposited coating included a Ta transition layer and a Ta-C composite outer layer. The thickness of the metallic Ta transition layer was approximately 400 nm, and the thickness of the Ta-C composite outer layer was approximately 2.9 μm. The initial contact resistance between the coating and the carbon paper was measured to be 12 mΩ·cm under a pressure of 1.2 MPa. 2 The corrosion resistance of the coating was evaluated under harsh conditions simulating PEM hydrogen production. The corrosion current density of the coating was measured to be 0.40 μA / cm² using potentiodynamic polarization. 2 The current density during the 24-hour potentiostatic polarization test was 0.50 μA / cm. 2 The surface contact resistance after testing was 400 mΩ·cm. 2 .

[0034] Example 3 This example, as a preferred embodiment of the present invention, discloses a functional coating with low contact resistance and high corrosion resistance and its preparation method. The only change is the sputtering current of the graphite target, and the outer layer has a Ta element content of 86% and a C element content of 14% by atomic percentage.

[0035] In this embodiment, the sputtering currents for the Ta target and the graphite target were 5.0 A and 1.4 A, respectively. The deposited coating included a Ta transition layer and a Ta-C composite outer layer. The thickness of the metallic Ta transition layer was approximately 400 nm, and the thickness of the Ta-C composite outer layer was approximately 3.1 μm. The initial contact resistance between the coating and the carbon paper was measured to be 18 mΩ·cm under a pressure of 1.2 MPa. 2 The corrosion resistance of the coating was evaluated under harsh conditions simulating PEM hydrogen production. The corrosion current density of the coating was measured to be 0.49 μA / cm² using potentiodynamic polarization. 2 The current density during the 12-hour potentiostatic polarization test was 1.77 μA / cm. 2 The surface contact resistance after testing was 576 mΩ·cm. 2 .

[0036] Example 4 This example, as a preferred embodiment of the present invention, discloses a functional coating with low contact resistance and high corrosion resistance and its preparation method. The only change from Example 1 is that the metal Ta is replaced with the metal Nb. The outer layer has an Nb element content of 95.6% and a C element content of 4.4% by atomic percentage.

[0037] In this embodiment, the sputtering currents for the Nb target and the graphite target were 5.0 A and 0.6 A, respectively. The deposited coating included an Nb transition layer and an Nb-C composite outer layer. The thickness of the metallic Nb transition layer was approximately 300 nm, and the thickness of the Nb-C composite outer layer was approximately 2.1 μm. The initial contact resistance between the coating and the carbon paper was measured to be 25 mΩ·cm under a pressure of 1.2 MPa. 2 The corrosion resistance of the coating was evaluated under harsh conditions simulating PEM hydrogen production. The corrosion current density of the coating was measured to be 0.130 μA / cm² using potentiodynamic polarization. 2 The current density during the 24-hour potentiostatic polarization test was 0.14 μA / cm. 2 The surface contact resistance after testing was 179 mΩ·cm. 2 .

[0038] Example 5 This example, as a preferred embodiment of the present invention, discloses a functional coating with low contact resistance and high corrosion resistance and its preparation method. The only change from Example 1 is that the metal Ta is replaced with metal Zr. The outer layer has a Zr element ratio of 91.2% and a C element ratio of 8.8% by atomic percentage.

[0039] In this embodiment, the sputtering currents for the Zr target and the graphite target were 5.0 A and 0.8 A, respectively. The deposited coating included a Zr transition layer and a Zr-C composite outer layer. The thickness of the metallic Zr transition layer was approximately 350 nm, and the thickness of the Zr-C composite outer layer was approximately 2.6 μm. The initial contact resistance between the coating and the carbon paper was measured to be 42 mΩ·cm under a pressure of 1.2 MPa. 2 The corrosion resistance of the coating was evaluated under harsh conditions simulating PEM hydrogen production. The corrosion current density of the coating was measured to be 1.10 μA / cm² using potentiodynamic polarization. 2 The current density during the 24-hour potentiostatic polarization test was 2.90 μA / cm². 2 The surface contact resistance after testing was 460 mΩ·cm. 2 .

[0040] Comparative Example 1 This example, as a comparative example of the present invention, discloses a functional coating with low contact resistance and high corrosion resistance and its preparation method. The only change is the sputtering graphite target current, and the outer layer has a Ta element content of 99% and a C element content of 1% by atomic percentage.

[0041] In this embodiment, the sputtering currents for the Ta target and the graphite target were 5.0 A and 0.3 A, respectively. The deposited coating included a Ta transition layer and a Ta-C composite outer layer. The thickness of the metallic Ta transition layer was approximately 400 nm, and the thickness of the Ta-C composite outer layer was approximately 2.4 μm. The initial contact resistance between the coating and the carbon paper was measured to be 10 mΩ·cm under a pressure of 1.2 MPa. 2 The corrosion resistance of the coating was evaluated under harsh conditions simulating PEM hydrogen production. The corrosion current density of the coating was measured to be 0.21 μA / cm² using potentiodynamic polarization. 2 The current density during the 24-hour potentiostatic polarization test was 0.67 μA / cm. 2 After testing, the surface contact resistance was >1000 mΩ·cm 2 .

[0042] Comparative Example 2 This example, as a comparative example of the present invention, discloses a functional coating with low contact resistance and high corrosion resistance and its preparation method. The only change is the sputtering graphite target current, which is based on Example 1. The outer layer has a Ta element content of 69% and a C element content of 31% by atomic percentage.

[0043] In this embodiment, the sputtering currents for the Ta target and the graphite target were 5.0 A and 2.0 A, respectively. The deposited coating included a Ta transition layer and a Ta-C composite outer layer. The thickness of the metallic Ta transition layer was approximately 400 nm, and the thickness of the Ta-C composite outer layer was approximately 3.6 μm. The initial contact resistance between the coating and the carbon paper was measured to be 154.6 mΩ·cm under a pressure of 1.2 MPa. 2 The corrosion resistance of the coating was evaluated under harsh conditions simulating PEM hydrogen production. The corrosion current density of the coating was measured to be 4.30 μA / cm² using potentiodynamic polarization. 2 The current density during the 24-hour potentiostatic polarization test was 15.2 μA / cm. 2 After testing, the surface contact resistance was >5000 mΩ·cm. 2 .

[0044] Comparative Example 3 This example, as a comparative example of the present invention, discloses a functional coating with low contact resistance and high corrosion resistance and its preparation method. The only change from Example 1 is that the metal Ta is replaced with the metal Nb. The outer layer has an Nb element content of 67% and a C element content of 33% by atomic percentage.

[0045] In this embodiment, the sputtering currents for the Nb target and the graphite target are 5.0 A and 3.0 A, respectively. The deposited coating includes an Nb transition layer and an Nb-C composite outer layer. The thickness of the metallic Nb transition layer is approximately 400 nm, and the thickness of the Nb-C composite outer layer is approximately 3.1 μm. The initial contact resistance between the coating and the carbon paper was measured to be 92 mΩ·cm under a pressure of 1.2 MPa. 2 The corrosion resistance of the coating was evaluated under harsh conditions simulating PEM hydrogen production. The corrosion current density of the coating was measured to be 2.5 μA / cm² using potentiodynamic polarization. 2 The current density during the 24-hour potentiostatic polarization test was 9.6 μA / cm. 2 After testing, the surface contact resistance was >10000mΩ·cm 2 .

[0046] The above are the embodiments listed in this example. However, this example is not limited to the optional embodiments described above. Those skilled in the art can arbitrarily combine the above methods to obtain other various embodiments. Anyone can derive other various forms of embodiments based on the inspiration of this example. The above specific embodiments should not be construed as limiting the scope of protection of this example. The scope of protection of this example should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A functional coating with low contact resistance and high corrosion resistance, characterized in that: It includes a transition layer and an outer layer, wherein the outer layer is a corrosion-resistant metal containing carbon.

2. The low contact resistance and high corrosion resistance functional coating according to claim 1, characterized in that: The corrosion-resistant metal accounts for 67-99% of the total metal content and carbon content accounts for 2-33% of the total carbon content.

3. The low contact resistance and high corrosion resistance functional coating according to claim 1, characterized in that: The corrosion-resistant metal is at least one of the metal elements Nb, Ta, Zr, or Hf.

4. The low contact resistance and high corrosion resistance functional coating according to claim 1, characterized in that: The metal of the transition layer is one or more of Zr, Nb, Ta, and Hf.

5. The low contact resistance and high corrosion resistance functional coating according to claim 1, characterized in that: The transition layer is coated on the bipolar plate.

6. The low contact resistance and high corrosion resistance functional coating according to claim 5, characterized in that: The bipolar plate is a titanium bipolar plate.

7. A method for preparing a functional coating with low contact resistance and high corrosion resistance according to any one of claims 1-6, characterized in that: The preparation method is DC magnetron sputtering.

8. The method for preparing a functional coating with low contact resistance and high corrosion resistance according to claim 7, characterized in that: The DC magnetron sputtering includes the following steps: A transition layer is prepared on a bipolar plate by sputtering a metal target, and then an outer layer is deposited by co-sputtering a metal target and a graphite target, or a metal target and a metal / graphite composite target, or a metal / graphite composite target.

9. The method for preparing a functional coating with low contact resistance and high corrosion resistance according to claim 8, characterized in that: Before sputtering the transition layer, the bipolar plate is etched under vacuum conditions using Ar plasma, and Ar is used as the working gas during the sputtering of the transition layer.

10. The method for preparing a functional coating with low contact resistance and high corrosion resistance according to claim 9, characterized in that: When performing Ar plasma etching on bipolar plates, either an ion source-assisted method or a method of applying a high negative bias voltage to the bipolar plates can be used, with the bias voltage being less than -450V.

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